1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition and, more particularly, to a radiation-sensitive resin composition suitable as a chemically amplified positive-tone resist and a chemically amplified negative-tone resist for ultra-microprocessing using various types of radiation such as ultraviolet radiation, deep ultraviolet radiation, X-rays, and charged particle rays.
2. Description of the Background Art
In the field of microfabrication represented by fabrication of integrated circuit devices, the design rules have become more and more minute in order to achieve higher integration. In recent years, development of a lithographic process enabling high accuracy microfabrication with a line width of 0.3 μm or less in a stable manner has been strongly demanded.
However, it is difficult to form such a fine pattern with high accuracy using a conventional method which utilizes visible rays (wavelength: 700–400 nm) or near ultraviolet rays (wavelength: 400–300 nm). To deal with this problem, a lithographic process using radiation with a shorter wavelength (wavelength: 300 nm or less) which can achieve a wider depth of focus and is effective for ensuring design rules with minimum dimensions has been proposed.
As a lithographic process using radiation with a short wavelength, processes using deep ultraviolet rays such as a KrF excimer laser (wavelength: 248 nm) or an ArF excimer laser (wavelength: 193 nm), X-rays such as synchrotron radiation, and charged particle rays such as ultra-deep ultraviolet rays or electron beams have been proposed. International Business Machines Corporation (IBM) has proposed a “chemically-amplified resist” as a resist exhibiting high resolution for such short wavelength radiation. At present, improvement of the chemically amplified resist is actively being undertaken.
The chemically-amplified resist contains a photoacid generator which generates an acid upon irradiation (hereinafter called “exposure”). Chemical changes in the resist film (changes in polarity, breakage of a chemical bond, cross-linking reaction, etc.) caused by the catalytic action of an acid changes solubility of the exposed area in a developer. A pattern is formed utilizing this phenomenon.
As such a chemically-amplified resist exhibiting comparatively good resist performance, a resist comprising a resin in which an alkali affinitive group in an alkali-soluble resin is protected by a group such as a ketal group (Japanese Patent Application Laid-open No. 140666/1995) or an acetal group (Japanese Patent Applications Laid-open No. 161436/1990, No. 249682/1993), a resist comprising a copolymer containing a t-butoxy(α-methyl) styrene unit, hydroxy(α-methyl) styrene unit, and t-butyl (meth)acrylate unit (Japanese Patent Application Laid-open No. 211258/1992), and the like are known.
However, since these chemically-amplified resists have peculiar problems, various problems in putting these resists to practical use for microfabrication with a design line width of 0.25 μm or less have been pointed out.
One serious problem is a change in the resist patterns such as a change in the line width or change into T-character configuration according to post exposure delay (PED), which is a period of time from exposure to post bake.
In recent years, the device structure has become more and more complicated. This requires a resist with excellent processing performance for narrow space (dark field) patterns of which the space width is narrower than an ordinary line width.
Another problem brought about by microprocessing and complication of lithographic processes is an iso-dense bias, which is a critical dimension (CD) difference between isolated patterns and dense patterns.
An object of the present invention is to provide a radiation-sensitive resin composition useful as a positive-tone or negative-tone chemically amplified resist, effectively responding to various radiations, exhibiting excellent resolution and pattern configuration, the pattern configuration and line width being affected by PED to a minimal extent, particularly excelling in narrow space processing performance, a minimal iso-dense bias, CD uniformity in various pattern designs, and capable of forming fine patterns at a high precision and in a stable manner.